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Topic: Why are fuses called fuses? (Read 1 time) previous topic - next topic


I have found many links that describe how to set fuses, but none (so far) that explains what fuses actually are. Can they be seen as some sort of basic configuration switches ("on chip dip switches" ;-) )? And why are they called "fuses". I only knew one meaning of the word "fuse" so far: protection against excessive current. I found that confusing.


Originally, programmable chips that were writeable in the field had actual metal links on the IC, that you "blew" (melted, exactly like an electrical fuse!) to write the value.  (thus, you could only write them once.)  This is also where the term "burn" comes from.  The terms have survived for small amounts of programmable bits (smaller than a "memory") , even though the technology has mostly moved on (I'm pretty sure AVR fuse bits are flash or EEPROM.)



I'm pretty sure AVR fuse bits are flash or EEPROM.
"Flash" - EEPROM - there is a difference?

AFAIK, the EEPROM, the program memory and the fuses are essentially identical.


"Flash" - EEPROM - there is a difference?
Originally, I think EEPROM has a different internal memory cell structure (more transistors.)  But marketing-speak has blurred the line, and I'm not sure whether that's true any longer.  What DOES tend to be true is that things called "flash" memory usually need to be erased a "page" at a time before they can be written, while EEPROM can be changed on a single-byte level.

Coding Badly

(I'm pretty sure AVR fuse bits are flash or EEPROM.)
They are Flash.

The signature line is also Flash (meaning exactly what you think that means.  :smiley-twist:)


(Did you figure out how to write new parameters in the "read only" fuse areas (signature, clock calibration default, etc)?  I'd heard that that was possible, but ever saw details.)

Coding Badly

I read about it.  Probably on AVR Freaks.  The commands are a logical extension of the read/write Flash commands.  The theory is that each processor has to be told what it is (I dub thee an ATmega328P).

Let me know if you would like me to hunt down the details.

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